Solid State light sources based on light emitting diode (LED) technology offer the promise of energy savings over incandescent and fluorescent lighting without the toxic materials utilized in fluorescent or organic light emitting diode (OLED) light sources.
However to achieve widespread adoption and acceptance of solid state lighting (based on inorganic LEDs) requires that it be competitively priced to compete with incandescent and mercury filled fluorescent light sources. Even with its greener attributes and favorable impact on the environment the average consumer will still make purchase decisions based on the initial cost of the light source. It matters not that a solid state light source will last longer than an incandescent or fluorescent light source and that it offers the promise of being more economical when factoring in the energy saved over its useful life. Most consumers are not willing to pay more (initially) for eventual savings later. However, reducing the cost of solid state light sources has been a big challenge for lighting companies. According to The U.S. Department of Energy, 70% of the cost of solid state light sources is due to the LED package (40%) and the appended heat sink (30%). In U.S. Published Patent Application No. 20130099264 (Livesay), which is commonly assigned and incorporated by reference into this invention, and previous filings by the authors of this invention, it was shown how both of these can be eliminated by combining the heat sink and package into the light emitting and heat dissipating element. Also shown were several ways in which this can be accomplished including making the thermally conductive luminescent material the wavelength conversion material or alternatively placing the wavelength material between the thermally conductive translucent material and LED. Livesay lists several materials that can be used for the thermally conductive translucent material or element, which become light emitting (i.e. luminescent) by directing the light from the LED into and through the translucent elements. Prior to this invention it was believed that to achieve high efficiencies (light output versus energy input) required translucent materials with high optical transparency. However, to achieve high transparency in ceramic materials usually requires more expensive processing. For example to achieve higher transparency in Cerium doped Yttrium Aluminum Garnet requires high sintering temperatures and subsequent hot isostatic pressing. Similarly, Al2O3 (alumina) becomes more transparent with more costly sintering and hot isostatic pressing. These processes increase the cost of the material used for the light sources as practiced in Livesay and this invention. To effectively cool via natural convection and radiation requires large surface areas of the light transmissive thermally conductive materials (as taught by Livesay) to dissipate the heat generated by the LEDs attached to them. However if the cost of processing the light transmissive thermally conductive materials is high, this becomes a significant factor in the cost of the light source. It would be beneficial if there was a way in which less expensive light transmissive thermally conductive or translucent materials could be used. This would lower the cost of the light sources and speed up adoption of these environmentally friendly sources.
Heat generated within the LEDs and phosphor material in typical solid state light sources is transferred via conduction means to large appended heat sinks usually made out of aluminum or copper. The temperature difference between the LED junction and heat sink can be 40° C. to 50° C. The temperature difference between ambient and the surfaces of an appended heat sink's surfaces is typically very small given that there is typically a significant temperature drop (thermal resistance) between the LED junction and the heat sink surfaces. With small temperature differences between the heat sink and ambient very little radiative cooling takes place. This small temperature difference not only eliminates most of the radiative cooling but also requires that the heat sink be fairly large (and heavy) to provide enough surface area to effectively cool the LEDs. The larger the heat sink, the larger the temperature drop between the LED junction and the surface of the heat sink fins. For this reason, heat pipes and active cooling is used to reduce either the temperature drop or increase the convective cooling such that a smaller heat sink volume can be used. In general, the added weight of the heat sink and/or active cooling increases costs for shipping, installation, and in some cases poses a safety risk for overhead applications. It would be advantageous if the heat sink temperature was close to the LED junction temperature to enable more radiative cooling of the light source.
Unlike conventional incandescent, halogen and fluorescent light sources, solid state light source are not typically flame resistant or even conform to Class 1 or Class A building code requirements. There are two types of fire hazards: indirect (where the lamp/fixture is exposed to flames) and direct (where the lamp/fixture itself creates the flames). Conventional solid-state lamps and fixtures can pose both indirect and direct fire threats because they use large quantities of organic materials that can burn.
Even though the LED die are made using inorganic material such as nitrides or AlInGaP which are not flammable, these LED die are typically packaged using organic materials or mounted in fixtures which contain mostly organic materials. Organic LEDs or OLEDs are mostly organic and also contain toxic materials like heavy metals like ruthenium, which can be released if burned. Smoke generated from the burning of these materials is toxic and one of the leading causes of death in fires due to smoke inhalation. Incandescent and fluorescent lighting fixtures typically are composed of sheet metal parts and use glass or flame retardant plastics designed specifically to meet building code requirements.
As an example, solid-state panel lights typically consist of acrylic or polycarbonate waveguides, which are edge lit using linear arrays of LEDs. A couple of pounds of acrylic can be in each fixture. Integrating these fixtures into a ceiling can actually lead to increased fire hazard. Other troffer designs rely on large thin organic films to act as diffusers and reflectors as seen in recent LED troffer designs. During a fire these organic materials pose a significant risk to firefighters and occupants due to smoke and increased flame spread rates. In many cases, the flame retardant additives typically used to make polymers more flame retardant that were developed for fluorescent and incandescent applications negatively impacts the optical properties of waveguides and light transmitting devices. Class 1 or Class A standards cannot be met by these organic materials. As such a separate standard for optical transmitting materials UL94 is used in commercial installations. The use of large amounts of these organic materials in conventional solid-state light sources greatly increases the risks to firefighters and occupants due to their high smoke rate and tendency to flame spread when exposed to the conditions encountered in a burning structure. A typical commercial installation with a suspended ceiling contains 10% of the surface area as lighting fixtures. The ceiling tiles are specifically designed to act as a fire barrier between the occupants and the plenum above the suspended ceiling. The lighting fixtures compromise the effectiveness of this fire barrier by providing a pathway for flames to bypass the ceiling tiles. For this reason even incandescent and fluorescent fixtures are typically required to have additional fire resistant covers on the plenum side of the ceiling. These fire enclosures increases costs and eliminates the ability to effectively cool the light fixture from the plenum side of the ceiling. Given that most solid state troffers depend on backside cooling these fire enclosures lead to higher operating temperatures on the LED die and actually increase the direct fire hazard for solid state light sources. The large amount of organics in the solid state light fixtures can directly contribute to the flame spread once exposed to flames either indirectly or directly.
The need therefore exists for solid state lighting solutions which are Class 1 rated which can reduce the risks to occupants and firefighters during fires and minimize the direct fire hazard associated with something failing with the solid state light bulbs.
The recent recalls of solid-state light bulbs further illustrate the risks based on the solid-state light sources themselves being a direct fire hazard. In the recalls, the drive electronics over-heated, which then ignited the other organic materials in the light source.
The need exists for solid state light sources which will not burn or ignite when exposed to high heat and even direct flames.
Existing incandescent and fluorescent lighting fixtures have over the last several decades found that the ideal solution is to construct the majority of the fixture using inorganic materials and to maximize the lumens per gram of the source. A typical incandescent source emits greater than 30 lumens per gram and the source is self cooling based on both convective cooling and radiative cooling. A conventional solid-state light bulb emits less than 5 lumens per gram and requires heatsinking means to transfer the heat generated by the LEDs and drive electronics to the surrounding ambient. The high lumen per gram in the incandescent and fluorescent bulbs translates directly into less material to burn both indirectly and directly. Also, in solid-state light bulbs the drive electronics and light source have the same cooling path and therefore heat generated in the drive electronics is added to the heat generated by the LEDs. The added heat from the LEDs elevates the temperature of the drive electronics and vice versa. In the recalls this has led to catastrophic results igniting the organic materials used in the solid state light sources. The coupling of the heat from the drive electronics and the LEDs combined with the large quantity of organic materials used creates a direct fire hazard when components like polymer capacitors overheat and burn. Based on years of effort the incandescent and fluorescent sources have moved away from organic based materials for exactly the reasons illustrated above.
The solid state lighting industry needs to develop high lumen per gram solid state light sources, which not only improve efficiency but also do not represent a fire hazard either indirectly or directly.
Commercial light applications are also subject to seismic, acoustic, and aesthetic requirements. Seismic standards require that suspended ceilings withstand earthquake conditions and more recently these same requirements are being used to address terrorist attacks. In general, lighting fixtures must be separately suspended from the overhead deck in suspended ceiling applications because of their weight and size.
The need exists for solid state lighting solutions, which can be integrated and certified with suspended ceilings.
Regarding acoustics the suspended ceiling dampens noise levels by forming barrier in a manner similar to the fire barrier previously discussed. The lighting fixtures again compromise the barrier created by the ceiling tiles because they cannot be directly integrated into the ceiling tiles or grid work.
The need exists for solid state lighting sources, which do not degrade the acoustic performance of the ceilings.
Lastly, lighting is aesthetic as well as functional. Market research indicates that troffers while functional are not desirable from an aesthetic standpoint.
The need therefore exists for solid state lighting sources, which provide a wider range of aesthetically pleasing designs.
Suspended ceiling represent a large percentage of the commercial, office and retail space. In this particular application 2 foot×2 foot and 2 foot×4 foot grids are suspended from the ceiling and acoustic/decorative tiles are suspended by the t shaped grid pieces. Lighting has typically been 2×2 or 2×4 troffers, which similarly are suspended on the T shaped grid pieces. The troffers are wired to the AC bus lines above the suspended ceiling. Each troffer consists of a sheet metal housing, driver, light sources, and reflective and diffusive elements. In the case of solid state troffers additional heatsinking means or cooling means may also be incorporated into each troffer. To comply with building codes most fixtures require additional fire containment housings, which isolate the lighting fixture from the plenum space above the suspended ceiling. In general a standard troffer requires a minimum volume of 1 cubic foot for a 2×2 and 2 cubic feet for a 2×4. The typical lumen output is 2000 lumens for a 2×2 troffer and 4000 lumens for a 2×4. In many instances the location of the light fixtures are put on a regular spacing even though uniform lighting throughout the area may not be required or desirable. This is driven by the difficulty and costs associated with relocating the troffers once installed. This leads to excess lighting with its associated energy losses.
The need exists for lightweight diffuse and directional lighting fixtures for suspended ceilings that can be relocated easily and upgraded or changed as technology advances.
Recently Armstrong has introduced its 24 VDC DC FlexZone grid system. The T-shaped grid pieces provide 24 VDC connections on both the top and bottom of the grid pieces. The availability of 24 VDC eliminates the need for a separate drivers and ballasts for solid state lighting. The elimination or simplification of the driver allows for very lightweight and low volume light fixtures especially for the cases where self cooling solid state light sources are employed. Lightweight and low volume translate directly into reduced raw material usage, fixture cost, warehousing costs, and shipping costs. By eliminating fixed metal housings and replacing them with modular and interchangeable optical and lighting elements that directly attach to an electrical grid system like Armstrong's DC FlexZone system costs can be reduced not only for the fixture itself but also for the cost associated with changing the lighting. Close to 2 billion square feet of commercial and retail suspended ceiling space is remodeled or created each year.
The need exists for more flexibility in how this space can be reconfigured.
Present fixtures require addition support to the deck of the building due to weight and size constraints per seismic building codes.
The need exists for field installable and user replaceable lighting fixtures that can be seismically certified with the grid so that the end user can adjust and reposition fixtures as the need arises.
Under the present requirements, any changes to the lighting requires that the ceiling panels be removed and at a minimum additional support wires must be installed to the building deck before the fixture can be repositioned. This may also require a reinspection of the ceiling in addition to the added cost for the change.
The need exists for lightweight, robust lighting that can be easily adjusted by the end user without the need for recertification and outside labor.
In evaluating the weight of light modules it is useful to utilize the concept of lumens per gram. Reducing the lumens per gram of light fixtures can have a major impact on manufacturing costs, shipping costs, and storage costs due to reduce materials costs and handling costs. It could also allow for fixtures which can be directly attached to the grid of a suspended ceiling and still meet seismic standards without requiring additional support structures which are commonly needed for existing troffer type light sources.
The need also exists for aesthetically pleasing high lumen per gram light fixtures.
For many applications the lighting should be present but not draw attention to itself. This is not the case with troffers, which immediately draw attention away from the other parts of the ceiling.
Therefore, there is a need for lightweight and compact lighting fixtures which address the above needs in suspended ceiling applications.
Again the thickness of the lighting module has a direct impact on the aesthetics of the installation. Existing linear solid state sources require large mixing chambers to spread the light emitted by the LEDs, which dramatically increase the depth of these light sources. In order for light panel modules to have a an emitting surface close to the plane of the ceiling and not to protrude into the room or office space below, the major portion of the light source module must be recessed into the suspension ceiling.
The need exists for low profile, or thin lighting panels with thicknesses under 10 mm, which are attachable to the electrified grids.
Ideally these lighting panels would be field replaceable from the office space side of the installation by end users (and not require custom installers) and present an aesthetically pleasing and monolithic and uniform appearance. Essentially the ideal suspension ceiling lighting system would “disappear” into the ceiling from an aesthetic standpoint.
Finally the need exists for solid state lighting sources, which can meet or exceed Class 1 or Class A standards, meet seismic requirements, meet acoustic standards, be field adjustable, and be easily integrated in an aesthetically pleasing manner into commercial lighting applications.
This invention discloses self cooling solid state light sources which overcome these issues.